1. Field of the Invention
The present invention relates to a recording tape cartridge which rotatably accommodates a reel onto which recording tape, such as a magnetic tape or the like, is wound.
2. Description of the Related Art
Recording tapes such as magnetic tapes and the like are used as external recording media for computers and the like. “One-reel” recording tape cartridges, which rotatably accommodate a single reel onto which a recording tape is wound, take up little space when stored and can record large amounts of information, and are employed as such recording tapes.
Such a recording tape cartridge is equipped with a brake structure such that the reel does not rotate inside the case at times of non-use (see, for example, the specification of Japanese Patent No. 3,187,022). A recording tape cartridge equipped with this brake structure is now described with reference to FIGS. 13 and 14.
In a recording tape cartridge 200 shown in FIG. 13, a single reel 204 is accommodated in a case 202. The case 202 is provided with a gear aperture 206 and a rotation-limiting rib 208. The gear aperture 206 is formed at a central portion of a floor plate 202A of the case 202. The rotation-limiting rib 208 protrudes downward from a ceiling plate 202B of the case 202.
The reel 204 is provided with a reel hub 210, which is formed in a circular tube shape with a base, around an outer peripheral portion of which recording tape is wound. At a lower face of abase portion 210A of the reel hub 210, a reel gear 214 is formed in an annular shape. The reel gear 214 is meshable with a driving gear 212A, which is formed at a rotation shaft 212 of a drive device. Insertion through-holes 216, which penetrate through the base portion 210A, are provided at a plurality of locations on a circular periphery, at the portion at which the reel gear 214 is formed. The insertion through-holes 216 are equidistant. A diameter of each insertion through-holes 216 is set to be larger than a gear pitch of the reel gear 214, and teeth of the reel gear 214 are not provided in a vicinity of each insertion through-hole 216.
At an upper face of the base portion 210A of the reel hub 210, engaging protrusions 218 are provided standing from (portions of) a plurality of locations along the predetermined circular periphery, between the insertion through-holes 216. Gear teeth 218A are formed at upper end portions of the engaging protrusions 218.
A disc-like brake member 220 is insertedly provided inside the reel hub 210. At a lower face of the brake member 220, an annular brake gear 220A is provided. The brake gear 220A is capable of meshing with the gear teeth 218A. A projection 222 is provided standing from an upper face of the brake member 220. The projection 222 is provided with an insertion groove 222A, into which the rotation-limiting rib 208 of the case 202 is inserted. When the rotation-limiting rib 208 enters this insertion groove 222A, the brake member 220 is rendered incapable of rotating relative to the case 202. Moreover, the brake member 220 is rendered movable only in a vertical direction, being guided by the rotation-limiting rib 208.
A compression coil spring 224 is disposed between the ceiling plate 202B of the case 202 and the brake member 220. Usually, the brake member 220 is urged downward by urging force of the compression coil spring 224, whereby the brake gear 220A is meshed with the gear teeth 218A. Thus, the brake member 220 is ordinarily in a rotation-locked state in which rotation of the reel 204 relative to the case 202 is blocked. Moreover, the reel 204 is pressed against the floor plate 202A of the case 202 by this urging force, and the reel gear 214 is exposed through the gear aperture 206.
Further, a release member 226 is disposed between the base portion 210A of the reel hub 210 and the brake member 220, so as to abut against the base portion 210A and the brake member 220. The release member 226 is formed in a plate form which does not interfere with the engaging protrusions 218, and is provided with leg portions 226A, which are respectively inserted into the insertion through-holes 216.
Thus, when the driving gear 212A is operated to mesh with the reel gear 214, as shown in FIG. 14, the leg portions 226A are pushed by the driving gear 212A, against the urging force of the compression coil spring 224, and the release member 226 is pushed upward. The release member 226 moves away from the base portion 210A and pushes the brake member 220 upward. Thus, meshing between the brake gear 220A and the gear teeth 218A is released. At this time, the reel 204 also rises relative to the floor plate 202A, and the reel 204 becomes rotatable inside the case 202.
The release member 226 has structure such that, in a state in which meshing of the driving gear 212A with the reel gear 214 is maintained, the leg portions 226A of the release member 226 are in contact with the driving gear 212A, and thus the release member 226 holds the brake member 220 at the release position described above.
Hence, the reel 204, whose reel gear 214 meshes with the driving gear 212A of the rotation shaft 212 when the rotation shaft 212 rotates, is a structure which rotates in the case 202. At this time, the release member 226 whose leg portions 226A are inserted into the insertion through-holes 216 of the reel 204 rotates integrally with the reel 204, and an axial center portion of the reel 204 rubs against (i.e., slidingly contacts) an axial center portion of the brake member 220.
Then, when the state of meshing of the driving gear 212A with the reel gear 214 is released, the brake member 220 is moved downward by the urging force of the compression coil spring 224, the brake gear 220A meshes with the gear teeth 218A, and the reel 204 is pushed against the floor plate 202A. As a result, the structure returns to the rotation-locked state in which rotation of the reel 204 relative to the case 202 is blocked.
The brake member 220 and release member 226 described above are both formed by resin-molding, such that complex forms can be produced with ease. In order to reduce rubbing resistance between the brake member 220 and the release member 226 when the reel 204 rotates, a portion of the brake member 220 that abuts (rubs) against the release member 226, which is an axial center portion of the brake member 220, is formed with a protrusion portion 220B, which is formed substantially in a spherical surface form. Thus, the brake member 220 is substantially in point contact with the axial center portion of the release member 226. Conversely, a portion of the release member 226 that abuts against the protrusion portion 220B of the brake member 220 is formed as a protrusion portion 226B, whose upper end is a flat surface. Thus, this structure has low susceptibility to occurrences of off-centering of the relatively rotating brake member 220 and release member 226.
Further, in order to effect a function of alignment between the brake member 220 and the release member 226, in addition to preventing this off-centering, a structure is known in which one of these abutting portions is formed as a convex surface and the other is structured as a concave surface with a greater diameter than the convex surface (see, for example, Japanese Patent Application (JP-A) No. 2000-331454).
Anyway, in recent years, increases in recording density of the recording tape cartridge have been demanded. In response to these demands, for example, reducing thickness of the recording tape and lengthening an amount of the recording tape that is wound onto the reel has been considered. Further, in accordance with increases in speeds of writing information onto the recording tape and reading information that has been recorded onto the recording tape, increasing a drawing-out speed (feeding speed) of the recording tape has been considered. Accordingly, for the recording tape cartridge 200, measures to deal with a lengthening of a continuous rotation time of the reel 204 and an increase in rotation speed of the reel 204 have been demanded.
However, at the recording tape cartridge 200, during rotation of the reel 204, the protrusion portion 220B of the brake member 220 and the protrusion portion 226B of the release member 226, which are respectively resin members, rub against one another. Therefore, if the rotation speed of the reel 204 becomes greater (for example, a feeding speed of the recording tape of 6 m/s or more) and the duration of the rotation becomes longer, heat is generated by rubbing resistance, and thus there is a problem in that the protrusion portion 220B and the protrusion portion 226B will melt. This problem similarly arises in the structure of JP-A No. 2000-331454.
Further, although this is not shown in the drawings, a structure is also known in which the release member 226 is not provided (for example, JP-A No. 63-251983). The protrusion portion 220B of the brake member 220 is directly pushed by a release portion. The release portion is protrudingly provided at an axial center portion of the rotation shaft 212 and advances in through a through-hole which penetrates through the base portion 210A of the reel hub 210. Thus, the brake member 220 is pushed up, and the rotation-locked state of the reel 204 is released. In this structure too, the protrusion portion 220B and the drive device side release portion rub against one another during rotation of the reel 204, and are formed of resin materials. Therefore, under the usage conditions described above, there is a risk that the protrusion portion 220B or the release portion may begin to melt. Note that, similarly to the protrusion portion 226B, a surface of the release portion of the drive device that rubs against the protrusion portion 220B is a flat surface.
Accordingly, in order to suppress this generation of heat, a structure (for example, JP-A No. 2002-197833) has been considered in which a portion corresponding to the protrusion portion 226B of the release member 226 is structured of a metallic material. Thus, rubbing resistance between the metallic material and the protrusion portion 220B, which is a resin material, is reduced. In this structure, the generation of heat in accordance with rubbing resistance between the protrusion portion 220B and the protrusion portion 226B is suppressed, and melting of the resin material protrusion portion 220B is prevented.
However, in the structure disclosed in JP-A No. 2002-197833, under conditions in which the rotation speed of the reel 204 has been increased and the rotation duration has been lengthened as described earlier, there is a problem in that the spherical surface-form protrusion portion 220B, which is the resin side, is abraded or worn down (crushed), and height thereof becomes lower. JP-A No. 2002-197833 further discloses a structure in which a metallic sphere is fitted in at the brake member 220 to form the surface abutting against the release member 226. However, for such a case, diameter of the metallic sphere, the form of the abutting surface of the release member 226 which is the opposite member, and the like are not described at all. That is, in the structures of JP-A No. 2002-197833, melting, abrasion or the like does not occur at the resin side abutting portion under predetermined conditions (i.e., conditions such that a magnetic tape which has been drawn out 10 metres from the case is wound back onto the reel in the case by an operation of 25,000 revolutions), but abrasion or wearing of the resin side abutting portion under conditions in which the rotation speed of the reel 204 has been increased and the rotation duration has been lengthened, corresponding to conditions of use which are expected hereafter, has not been considered at all, and such abrasion or the like cannot be prevented.
Thus, if melting of the protrusion portion 220B and the protrusion portion 226B or abrasion of the protrusion portion 220B or the like occurs as described above, the brake member 220, which is urged by the compression coil spring 224, moves downward and an amount of insertion of the rotation-limiting rib 208 into the insertion groove 222A of the brake member 220 is reduced. At the projection 222 and the rotation-limiting rib 208 of the case 202, which are channel walls of the insertion groove 222A, draft angling is provided for die release at a time of resin-molding. Therefore, when the above-mentioned insertion amount decreases, a gap between an inner face of the projection 222 and the rotation-limiting rib 208 becomes larger, and this is a cause of looseness of the brake member 220 and the generation of noise during rotation of the reel 204. Further, in the recording tape cartridge 200 in which the protrusion portion 220B abuts against the protrusion portion 226B (i.e., a structure of Japanese Patent No. 3,187,022, JP-A No. 2000-331454 or JP-A No. 2002-197833), a reduction in the insertion amount causes looseness of the brake member 220 at times of non-use.